JDub Adventures Is Putting 30 Inch Tires on a Kei Truck: What That Actually Costs

A 24 inch tire is what came on the truck from the factory. JDub Adventures decided that was not enough. Part 1 of his Kei truck build series puts six extra inches of tire diameter on the menu, which sounds like a tire swap and is actually a complete drivetrain rework with a tire swap on top.

That gap between "buying a 30 inch tire" and "running a 30 inch tire" is where most ambitious off road builds die. The tires sit in the garage. The lift kit shows up. The fenders rub, the speedo lies, the brakes feel like a recommendation, and the truck spends a year in pieces. JDub is going to push through all of that on camera, which is the point of the series. But if you are thinking about following along on your own Daihatsu Hijet, be honest about what the math actually demands before you order parts.

The Geometry Problem

Stock kei trucks roll on 145/80R12 tires. That works out to about 24 inches of overall diameter and gives you roughly six inches of ground clearance between the diff and the dirt, according to the technical breakdown Kei Trucks published on 4WD tire sizing. The factory wheel wells are sized to clear exactly that.

A 30 inch tire adds six inches of diameter. Half of that goes up, half goes down. The down half raises ground clearance, which is the whole point. The up half is the problem, because the up half lives inside a stock fender well that was sized around a 24 inch tire. Without lifting the body or cutting metal, you have negative clearance.

To actually run the tire, you need somewhere around three inches of suspension lift to recover what the tire steals back from clearance, plus fender surgery to clear the upper sweep. Rough Country sells a 4.5 inch lift kit specifically for the Hijet Jumbo 4WD, which is the kit most of these extreme builds end up running. The product page openly states the kit tops out at 25 inch tires for fender clearance. Going to 30 means trimming the wheel arches, replacing the bumpers, or fabricating tube flares from scratch. That is not optional.

The Gear Ratio Tax

Here is the part that does not show up in the trailer for any of these builds. A 30 inch tire is 25 percent larger in diameter than a 24 inch tire. That means at any given engine RPM, the truck moves 25 percent faster. Which sounds like a gain until you remember the engine making that RPM is 660cc.

A stock Suzuki Carry or Hijet makes around 50 to 64 horsepower depending on the year and engine. The factory gearing is matched to the tire size and the power band. Stretch the gearing by 25 percent and first gear stops being a crawl gear and starts being a stall gear. Highway revs at 55 mph drop out of the engine's powerband and into a flat spot where the truck cannot hold speed up a hill, much less accelerate. You do not feel this on flat pavement. You feel it the first time you try to pull a steep grade with a load in the bed.

There is a fix. You can re gear the transfer case or swap to a lower final drive, but on a kei truck that means sourcing parts from a 4WD model with the right ratio, which is harder and more expensive than any of the visible mods. Most builders do not do it, and most builders complain later about how the truck drives. Oiwa Garage's lift guide calls this out directly: lifting beyond 2 to 3 inches starts compounding driveline angle, weight transfer, and gearing issues that the lift kit alone does not address.

What Else Quietly Breaks

The speedometer is geared to the stock tire, so it now reads 25 percent slow. Forty looks like thirty. That is a ticket if you do not correct it with a speedo gear or a recalibration module.

Brakes were sized for an 1,800 pound truck on 24 inch tires. Add a hundred pounds of tire and wheel at each corner and unsprung mass jumps. The factory drum brakes are adequate, not impressive, and they were never designed to haul down a tire this much heavier than stock.

CV joint angles get extreme with the lift. The drivetrain on a 4WD kei truck was geometrically designed around stock ride height, and the more you lift it, the more aggressive the axle to hub angle becomes during suspension travel. TFL Truck's write up on kei truck off road builds calls the lift kit a must, but the experienced builders they talked to all stop at modest heights for exactly this reason. Payload drops too. A heavier tire is dead weight before you load a single pound of cargo, which eats into the Hijet's 770 to 990 pound rating.

When the Build Is Actually Worth It

There is a real use case for this much truck. Deep snow country where stock tires are useless. Loose rock and washout terrain where ground clearance is the only thing between you and a broken oil pan. Content creation where the build itself is the point. Property owners with several hundred acres of trail and no plan to ever drive the truck on public road. The r/keitruck community has examples of builds where 28 to 30 inch tires earn their keep, and most of them are property trucks that never see a state inspection.

For everyone else, a 2 to 3 inch lift with 14 inch wheels running an aggressive all terrain tire in the 175/65R14 to 185/65R14 range gets you eight inches of ground clearance, keeps the speedo accurate, preserves the gearing, and does not require fender surgery. That is the build covered in our off road mods guide, and it is the build most owners should stop at.

The Bottom Line

JDub's series is a great watch precisely because the build sits at the edge of what a Hijet can structurally absorb. The lift, the fenders, the gear ratio, the brakes, the CV angles, the payload loss, every one of those costs time and money on camera. That is the entertainment.

But if you are spec'ing your own kei truck for serious off road use, the ceiling for a daily driveable build is closer to 25 inch tires than 30. Beyond that you are building a project vehicle, not a usable truck. The Hagerty primer on kei trucks is a decent starting point, and a solid pre purchase checklist will save you from buying a truck that is already too tired to absorb the build. The Honda Acty is the other obvious candidate platform if you want the same build profile on a different chassis.

When you are ready, the dealer directory covers shops that stock parts trucks and lift compatible imports. Before any of it, check the state legality guide for your state. A lifted Hijet on 30 inch tires is exactly the vehicle that gets pulled in for inspection where kei trucks are already borderline legal.